This proposal is to continue our previous investigations with spontaneously hypertensive rats (SHR) that have been raised at the University of Iowa. Recent findings show that early (at two weeks of age) exercise (50-60% max VO2) is associated with lower resting systolic pressures at the time (3 months) when the nontrained rats are borderline hypertensives (160-170 mmHg.). At six months of age, trained rats also have lower resting systolic pressures; however, it is because they had lower values three months earlier. Our intent is to follow training in animals receiving reduced dosages of anti-hypertensive drugs and determine whether the combination is sufficient for normalization purposes. Trained SHR groups also exhibit more of a fall in blood pressure when subjected to conditions of lower body negative pressure. These decreases are attributed in part to a change in baroreceptor sensitivity. Therefore, we intend to conduct experimental hemorrhage in trained and nontrained groups to determine if trained animals are at a greater disadvantage in this situation. Although there is considerable discussion on changes in wall thickness and wall/lumen ratios, there is a paucity of direct data on this topic as it pertains to training. Hence, we plan to continue our current research and examine these parameters in decending aortas, iliac, femoral and caudal arteries removed from perfused rats. To date, training does not appear to result in changes in these parameters. However, our numbers are small and the variability is large. With normotensive rats we are attempting to perfect the baroreceptor denervation technique of Kreiger. Our mild success rate is sufficiently encouraging for us to continue the procedure and to wait until sufficient animals are available for lower body negative pressure tests. We also want to train these animals before subjecting them to conditions of lower body negative pressure.